In all-optical wavelength-agile telecommunication networks, wavelength converters are used for converting the wavelength of an optical signal carrying a data packet in order to propagate the data packet into an appropriate channel. The selection of the appropriate channel is performed according to the destination address of the data packet. The destination address encoded in the data packet must first be read in order to determine the appropriate channel before converting the wavelength of the optical signal carrying the data packet to the appropriate wavelength corresponding to the appropriate channel. The determination of the appropriate channel and the wavelength conversion represent time-consuming processes. Therefore, a time delay must be introduced in the propagation of the optical signal in order to allow for the determination of the appropriate channel and the conversion of the optical signal to the appropriate wavelength.
In order to introduce a time delay in the propagation of the optical signal, delay lines, such as “slow light” devices, adapted to slow down the propagation speed of an optical signal can be used along with optical wavelength converters. For example, photonic crystals presenting slow light propagation modes can be used to reduce the propagation speed of the optical signal carrying the data packet while the appropriate channel is determined and the optical wavelength converter is adjusted to the appropriate wavelength. In another example, the slowing down of the optical signal may be achieved by first converting the optical signal into a phonon which has a reduced propagation speed with respect to that of light, and then converting the phonon back into an optical signal. The phonon may be generated via Brillouin scattering by propagating the optical signal into an adequate medium such as an optical fiber or a crystal for example. However, because the length of the photonic crystal or that of the Brillouin scattering medium is predetermined and fixed, such “slow light” devices usually introduce a fixed time delay for the propagation of the data packet.
Therefore, there is a need for an improved wavelength converter device having time delay capability.